A continuous vacuum deposition apparatus comprises a vacuum deposition chamber which is provided with seal roll means through which a metal strip to be plated can be hermetically introduced and let out and contains a metal evaporation apparatus and a guide roll or rolls for the metal strip. A typical such apparatus is disclosed in Japanese Laid-Open Patent Publication No. 18646/72.
The evaporation apparatus comprises an evaporation bath and a vapor channel, the opening of which is placed close to the surface of the metal strip to be plated.
A problem when a metal strip is plated by the continuous vacuum deposition process using such an apparatus is that the surface of the strip is not uniformly plated but usually both edge portions are thinly coated because the inside pressure of the vacuum deposition chamber is lower than the vapor pressure in the evaporation chamber and therefore there is a leak of metal vapor at the periphery of the opening of the vapor channel, which causes a non-uniform thickness distribution.
The object of the present invention is to provide a method which enables a deposited film to be formed as uniformly as possible, overcoming the defect of the prior art that the deposited film is thinner at both edges of the substrate strip.